850 Poor gas mileage - Tips to improve mpg...
 

I just replaced the O2 sensor on our our 97'850 R wagon, there is currently no code being thrown. We usually get around 20mpg and it has recently dropped to about 16. Do you guys have any ideas?


thanks,
Chet

was it a cheapo o2 or the OEM one?
What gas are you using?

OEM o2 sensor
we are using regular

chet

I didn't think our cars ran on regular gas. I always use premium gas.

1995 t5R

A lot of people do it but I use 93. The 87 is minimum.

Anywho, what is the condition of the car? When was the last time the car has been at stage 0?
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GAS MILEAGE ESTIMATES FROM VOLVO:
https://customers.volvocars.com/owne...release_3.html

Volvo claims that the NA 850 should get 20/28 mpg. The turbo models should get 19/26.

could be lots of things: dirty valves, clogged fuel injectors, wrong O2 sensor, etc...

My car got bad gas mileage when it was running rich.

what was causing it to run rich?

The last thread I read about someone having problems with their car running rich it was running cold because the t-stat was broken and open. Our temp gauges show normal temp at about 160 through 215. It should run at about 185-205 all the time. If you're running below 180 it could think it's still a little cold and run rich till it warms up to 180, which it never will.

I thought 87 octane was cool, if I need to change I will. I will check the temp and see if the thermostat is open all the time. we did move to a much colder environment recently, if that could have anything to do with it.

Thanks,
Chet

If you're running 87 octane, you're losing power due to the knock sensor sensing knock and retarding your timing. 87 octane WILL cause some knock in our cars....at least the turbos.

It was my car that was running rich due to the thermostat being stuck open and car taking a long time to warm up or sometimes not warming up at all. My gauge did at times move a little but, only went down to the cold mark when it was real cold out which most of the winter it was freezeing here in Baltimore. Put in a new thermostat and got crazy better gas mileage and car runs better. Drove it all the way to florida no problems.

Is your car a turbo?
My s70 t5 is giving awful mpg, i ask around in various forums and seems that its close to normal, I have found not much difference in mpg between 87 or 91 gas ( rather use 91)

But, this is what I am doing to see of mileage improves.
New plugs
91 oct Full gas tank
K&N air filter
Check tire pressure
Check alignment ( new suspension parts coming soon)
Sea Foam treatment
Oil change , mobil 1 synt.

In your case I would check rotor and cap, plug wires.

Seems like nowdays the fuel evaporates, or maybe its the money in the pocket the one that does..

Btw, my car is doing 14 to 16 pure city..

same mileage here, my wife drives the car pure city and gets about 15.5. I will do an oil change, and run the other suggestions that you guys recommended. Stage zero was performed on the car before we got it in 2009, about 20,000 miles ago. since then I have run sea foam, but not through the brake booster line into the intake manifold, I will try that as well. Thanks for the help guys, I will try those ideas.


Chet

I felt like both the s70 and the 850 sipped gas, I guess it has something to do with $20 worth of gas spewing out and today is not even a 1/4 tank..

My last 600 miles around town I've gotten 25.8 in my T-5R. I have NOT changed plugs yet, maybe in a few months unless I sell it.

Rspi

Man.. 25.8 I wish... What have you done to the car?
Town as in highways and stuff, or bumper to bumper like here..????

My trip computer has an average mph. Mine says 29 mph (far left). I was thinking the average mph was going to be more like 36. I'm going to reset it and start over. The only time I ever drive over 63 mph is to get someone's attention.

I really have not done anything to the car. I run full synthetic and change oil every 3 to 5k. I have a box K & N, I have NOT replaced my plugs or wires (they are oem). The wires are dated something like June 2007 so I think the plugs were likely replaced around then. In May '06 the car was registered at 73k, in April of '09 the car had 78k. So that car was only driven 5k in 3 years. Since then I have had the car parked for about 12 months here and there, and it now has 111k :). Other than that, I have been battleing tire pressure until Saturday when I replaced the wheels and tires. I believe the biggest thing I did was purchase a scan gauge II and used that to train my driving techiques to get better gas mileage. I think that has improved my mileage about 15%, maybe more. Best $169 I've ever spent on a car toy.

RSPI: very impressive

my wife says that she never uses the turbo. although I think her average speed is around 20 mph. The PCV system has never been touched, could that effect the mileage at all? I will replace the plugs, wires, dist cap, see where we are then. Thanks for the help guys.


chet